Hawaii's Kilauea volcano has erupted, causing lava to spew out of cracks in the ground in residential areas and prompting thousands of people to flee.

The Pacific island state's governor signed an emergency proclamation releasing disaster funds to the Big Island in the eruption's wake.

Local news footage showed streams of lava snaking through a forest and authorities reported "steam and lava emissions from a crack in Leilani Subdivision in the area of Mohala Street" following the blast.

Residents of that impacted area, some 1,700 people, were under mandatory evacuation after the burst from Kilauea, one of the most active volcanos in the world.

In addition to the obligatory evacuations, many areas fell under voluntary evacuation zones, affecting some 10,000 people, according to a local official.

A plume of ash rises from the Puu Oo vent on Hawaii's Kilaueaa volcano Credit: US Geolgogical Survey/AP

US Geological Survey authorities of the Hawaiian Volcano Observatory unit were both on the ground and headed into the air to assess the eruption.

It followed some 100 small earthquakes in recent days and began around 4.45 pm local time (2.45am GMT Friday), according to the agency.

Earlier, at 10.30 am, a larger 5.0-magnitude earthquake south of the Puu Oo volcano cone triggered rockfalls and potential collapse into a crater on the volcano, according to USGS.

The agency said those downwind of the dissipating plume "may experience a dusting of ash," warning of "potentially lethal concentrations of sulfur dioxide gas" in the zone as well as methane blasts that could propel large rocks and debris in adjacent areas.

Kilauea volcano - Hawaii - locator map

Governor David Ige activated the archipelago state's National Guard troops, and told residents to pay heed to warnings.

"Please be alert and prepare now to keep your family safe," Ige wrote on Twitter.

The danger is of such magnitude that it warrants preemptive and protective action in order to provide for the safety, health and welfare of the residents of Leilani Estates and surrounding areas.#HIGov#HINews@Hawaii_EMA@CivilDefenseHI

It emphasised that the early stages of fissure eruptions are "dynamic," and "additional vents and new lava outbreaks may occur."

"At this time it is not possible to say where new vents" could happen, it said.

Eruptions can take place without notice

The affected area is part of the Big Island's East Rift Zone, in which the Hawaii Volcano Observatory had "identified magma movement" and warned residents that seismic activities and eruptions could take place without notice.

"All areas bordering East Rift Zone at high risk for eruption," Hawaii County's mayor Harry Kim said on Twitter.

US Senator Brian Schatz of Hawaii said The Federal Emergency Management Agency (FEMA) was mobilising resources, as well as monitoring for forest fires, power outages and water supply issues.